Relative aromaticity in heteropolar inorganic analogs of benzene

Fink, William H.; Richards, James H.

doi:10.1021/ja00009a026

Cited by 100 publications

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“…Nevertheless, ASE calculations depend strongly on the equations used (isodesmic, homodesmotic, hyperhomodesmotic), the adopted reference molecules, and the computational levels and basis sets. For instance, while Fink and Richards used the ASE via homodesmotic reactions with trans configurations of the reference molecules for benzene (22.1 kcal mol -1 ) and borazine (11.1 kcal mol -1 ) [10] Schleyer et al obtained different values of the ASE using homodesmotic reactions for benzene (34.1 kcal mol -1 ) and borazine (10.0 kcal mol -1 ) [11] with cis configurations of the reference molecules.…”

Section: Introductionmentioning

confidence: 99%

Borazine: to be or not to be aromatic

et al. 2007

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Aromaticity of borazine, which has been subject of controversial discussions, is addressed. Beside a short review on aromaticity of borazine we report a detailed analysis of two molecular fields, the induced magnetic field (B ind ) and the electron localization function (ELF). The induced magnetic field of borazine shows a long-range shielding cone perpendicular to the molecular plane, as in benzene, but lower in magnitude. Contrary to benzene, borazine shows two weakly paratropic regions, one of them inside the ring, and the second one enveloping the boron atoms. It is necessary to separate r and p contributions to identify whether borazine exhibits p-aromatic character comparable to benzene. Nucleus-independent chemical shift (NICS) isolines show that the r electrons are much stronger localized than p electrons, their local paramagnetic contributions generate a short-range response and a paratropic (deshielding) region in the ring center (similar to an anti-aromatic response). Three regions can be identified as chemically meaningful domains exhibiting an internally strong electron delocalization (ELF = 0.823). Borazine may be described as a p aromatic compound, but it is not a globally aromatic species, as the electronic system is not as delocalized as in benzene.

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Section: Introductionmentioning

confidence: 99%

Borazine: to be or not to be aromatic

et al. 2007

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“…[10] This is also the case for the D 3h -symmetric borazine (B 3 N 3 H 6 ), which is known to be nonaromatic. [7] Each compound possesses 30 valence electrons.…”

Section: Resultsmentioning

confidence: 99%

“…Consequently, benzene is aromatic, whereas borazine is not. [7] Several isovalent electronic analogues can be considered, for instance, by moving down the periodic table (Si 6 H 6 , Ge 6 H 6 ). [8,9] Recently, the similarity between benzene and one form of methylaluminoxane, Al 3 O 3 Me 3 , [10] was discussed.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Studies of Aluminoxane Chains, Rings, Cages, and Nanostructures

Linnolahti

Luhtanen

Pakkanen

2004

Chemistry A European J

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Alumina nanostructures and three families of aluminoxanes, linear, cyclic, and cagelike structures, have structures that resemble their isovalent electronic hydrocarbon analogues. Specific examples of each family are the counterparts of fullerene, allene, benzene, and cubane, respectively. The aluminoxanes and alumina nanostructures are related to each other; the latter can be regarded as a hydrogen- or alkyl-free form of aluminoxane. By exploiting this relationship, the relative stabilities of the three families of aluminoxanes, alumina nanostructures, and alumina crystal lattices have been estimated. According to ab initio calculations, aluminoxane cages, which take the form of a truncated octahedron and related polyhedra, are favored. The stability of the preferred cage, T-symmetric Al28O28H28, is practically equal to that of the alpha-alumina crystal lattice.

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“…However, its chemical bonding is different: whereas benzene is aromatic, borazine has been classified as nonaromatic or marginally aromatic. [20][21][22][23][24][25][26] The aim of the present work is to evaluate, in an extreme situation, the validity of the concepts mentioned in the preceding paragraphs, in order to design new stable molecules. The chosen system to achieve this goal is [OsCl2(SC3H3)(PH3)2] + ,which presents some characteristics that make it suitable for this purpose: 1) it is a simplified model of the osmabicycles (aromatic compounds where one Os atom is present in five-membered metallacycles), studied both experimentally and theoretically by Esteruelas et al, 27 2) this system was classified as clearly aromatic, 28 with participation of Os-d-orbital (especially dxz and dyz orbitals) closing the circuit of π-orbitals and allowing electronic delocalization on the planar OsC3S fragment.…”

Section: Introductionmentioning

confidence: 99%